In the related art, when property and performance of a tire for truck, passenger vehicle, and another vehicle are measured, a rolling resistance of the tire is considered as one of important measurement items. The rolling resistance of the tire is a force in a tangential direction generated between the tire and the ground when the tire is rolled on the ground. A tire testing machine measures the rolling resistance of the tire as the force in the tangential direction generated between the test tire and a partner surface rotating in contact with the tire (for example, a surface of a load drum). That is, when a force (applied load Fz), which has a predetermined magnitude in a radial direction between the tire and the partner surface, is applied, a rolling resistance Fx is generated in response to the applied load Fz of the tire, and a relation between the applied load Fz and the rolling resistance Fx is measured.
Such a “rolling resistance measurement method” is a method performed by a drum-type tire traveling test machine, and is defined in Japanese Industrial Standard JIS D 4234 (passenger car, truck and bus tires—methods of measuring rolling resistance, 2009). JIS D 4234 defines four measuring methods of a “force method” of measuring the rolling resistance Fx with a tire spindle or obtaining a counterforce through a conversion, a “torque method” of measuring an input value of a torque when a rotation is applied to the tire by the load drum, a “coasting method” of obtaining a deceleration of assembly of the load drum and the tire, and a “power method” of obtaining a power input when a rotation is applied to the tire by the load drum. Even in a case where the rolling resistance of the tire is measured by any one of those methods, it is necessary to apply the large applied load Fz to the tire. Therefore, in order to measure the rolling resistance Fx smaller than the applied load Fz, a dedicated testing machine having a proper accuracy is necessary. For example, in the case of a passenger car, in a case where the applied load Fz is about 500 kgf, a magnitude of the rolling resistance Fx is a little less than about 10 kgf, and a dedicated testing device which can measure such a small rolling resistance Fx is already commercialized.
As such a rolling resistance testing machine, for example, a machine illustrated in Patent Reference 1 is known. The rolling resistance measuring device in Patent Reference 1, the tire is brought into compressive contact with an outer circumferential surface of a cylindrical load drum (traveling drum). The tire bears a spindle through a bearing, and the force applied in x, y, and z-axial directions and a torque (moment) are measured by a multiple component force detector of the spindle. In the device in Patent Reference 1, a correction is performed with respect to interference between those component forces, and then, a relation between the applied load Fz in an axial direction of the tire and the rolling resistance Fx is measured.
Patent Reference 2 discloses a method of predicting the rolling resistance of the tire based on a measurement result of the viscoelastic characteristics of various kinds of rubber members forming the tire and a numerical analysis based on FEM (Finite Element Method) model of the tire. The rolling resistance of the tire is calculated from the entire energy loss calculated from a product-sum operation of the deformation amounts of the various kinds of rubber members and the attenuation characteristics of the rubber members at the time of rotating the tire.